The present invention relates to a bending machine such as a press brake and its operation method, and in particular, to a bending machine that can detect an angle during bending.
Conventional bending machines such as press brakes measure a bend angle in line to control it during processing or determine whether or not the bend angle of processed work is appropriate. In these bending machines, an angle measuring instrument for measuring the bend angle in line is generally installed near an upper die and installed in and removed from a bent portion of the work using a measuring instrument inserting and removing mechanism. Some angle measuring instruments have been proposed which have an angle measuring instrument integrated into the upper die.
Some bending machines using the above described measuring instrument inserting and removing mechanism insert a corner contacting member shaped like a parallel link into the bent portion of a work such as a metal sheet and detect a bend angle by using a rotary encoder to measure displacement of a linear position of a linkage section occurring when the corner contacting member comes in contact with a corner forming surface of the work (Japanese Patent Publication Number 2630720). According to this patent, the measurement can be made substantially irrespective of the position of the work and regardless of the effect of variations in the thickness of the work or dimensions of opposite surface of a recessed corner of the work.
Since, however, the displacement of the linear position of the corner contacting member is converted into rotation of the encoder, a possible minor error in a motion converting section of the encoder limits measuring accuracy. Accordingly, it is difficult to further improve measuring accuracy. In addition, the needs for the measuring instrument inserting and removing mechanism in turn require the size of the entire measuring apparatus to be increased, so that it is difficult to install a plurality of angle measuring instruments in order to measure the angle at a plurality of locations spaced in a bending line direction of the work. Such measurements at a plurality of locations are desirable for obtaining through accuracy for bending.
Integrating the above described angle measuring instrument into the upper die facilities installation of angle measuring instruments at a plurality of locations, but due to its three-dimensional shape having certain length, breadth and depth dimensions, the rotary encoder cannot be integrated into a flat part such as the upper die of the press brake. The upper die of the press brake has a thickness of, for example, several millimeters and few angle measuring instruments that can be integrated into such a flat press die without affecting its strength have been used for practical applications.
Examples of proposed angle measuring instruments integrated into the upper die of the press brake insert two scanning elements of different widths into a recessed corner of work to bring opposite ends of each of the elements into contact with corresponding surfaces of the recessed corner and convert a difference in recessed corner advancing depth between the scanning elements, into a bend angle. Each of the scanning elements is shaped like a disc or a rod. The difference in advancing depth is detected by an optical sensor such as a PSD (Position Sensing Detector).
The optical sensor, however, is easily affected by heat and has its measuring accuracy reduced by heat generated during bending. In addition, since the upper die must have a split structure only to integrate the angle measuring instrument thereinto, the upper die has a complicated structure and has its strength reduced, thereby requiring the size of the upper die to be increased to compensate for the complicated structure and the reduced strength.
In addition, the bending of work involves a phenomenon called xe2x80x9cspring backxe2x80x9d where the bend angle is diminished, though slightly, due to the elasticity of the work, thereby precluding accurate detections or requiring a long period of time for detections. For example, to detect the bend angle after spring back, a bending load must be released. In this case, the position of the work may change and such a change in position must be flexibly dealt with. Consequently, the bending machine with an angle measuring instrument integrated thereinto must be improved and a method for effectively operating such a bending machine must be developed.
Other angle measuring instruments installed in the bending machine are applications of image processing, and irradiate a measured target with a slit light from a semiconductor laser and use a CCD camera to pick up an image of a bent portion to determine its bend angle. These measuring instruments, however, have their measuring accuracy significantly affected by variations in ambient brightness and require a complicated and expensive structure.
It is an object of the present invention to provide a bending machine that can build an angle measuring instrument into a mold to accurately measure an angle during bending.
It is another object of the present invention to enable the angle to be accurately measured without attenuating signals attenuation while eliminating the effects of variations in temperature using a simple structure.
It is yet another object of the present invention to allow an angle measuring instrument to be easily built into a mold by splitting the mold.
It is still another object of the present invention to provide a method for operating a bending machine wherein an angle measuring instrument built into an upper die is used to achieve accurate bending taking spring back into consideration.
The present invention provides a bending machine for carrying out bending by using a linearly extending male and female dies to sandwich a work therebetween, the bending machine being characterized in that the male die has an angle measuring instrument integrated thereinto for measuring a bend angle of the work bent by the male and female dies and the angle measuring instrument has an inductive linear position detector.
With this configuration, the angle measuring instrument is integrated into the male die to enable angle detections during bending. In addition, the angle measuring instrument advances into a bent portion of the work as the male die is elevated or lowered for bending or the like, thereby eliminating the needs for a mechanism exclusively used to drive the angle measuring instrument forward and backward. The angle measuring instrument has the inductive linear position detector, small accurate inductive linear position detectors have been used for practical applications and enable accurate angle detections when used in the angle measuring instrument. Such a linear position detector can also be easily integrated into a male die comprising a flat press die as in a press brake. Various inductive linear position detectors are available including differential transformers and phase shift detectors.
Specifically, the angle measuring instrument comprises a corner contacting member that comes in contact with opposite sides of a recessed corner resulting from the bending of the work to have its linear position displaced depending on an opening angle between corner forming surfaces and an inductive linear position detector for measuring displacement of the linear position of the corner contacting member.
The linear position detector preferably detects a change in linear position based on a change in phase angle and has a function for using an output from a plurality of coils or impedance means to compensate for a temperature characteristics of a coil for detecting the linear position.
When the position detection is based on a change in phase angle, the position can be accurately detected without being affected by signal attenuation. In addition when the linear position detector has a function for using an output from a plurality of coils or impedance means to compensate for a temperature characteristic of a coil for detecting the linear position, the position can be easily detected while eliminating the effects of variations in temperature. Thus, measurements can be made without being affected by heat generated during bending, thereby eliminating the needs for a correction corresponding to an operation time or the like.
Specifically, the linear position detector can be configured to have, for example, a plurality of coils excited by an in-phase alternating current (AC) signal, a magnetic responding member having its linear position displaced to change inductance of the coils, and an operation circuit. In this case, the operation circuit combines output voltages from the plurality of coils to generate a plurality of AC output signals to detect a phase angle corresponding to the displacement of the linear position based on the correlationship between amplitude values of the plurality of AC output signals.
The male die may be formed of a plurality of split dies arranged in a die width direction so that the die width can be changed by changing the number of arranged split dies. In this case, any ones of the split dies have an housing recess in side end surfaces thereof in which the angle measuring instrument is housed. If the recess is formed in the split surface of the split dies arranged in the die width direction and the angle measuring instrument is housed in this recess, then the splitting for changing the die width can be used to facilitate the integration of the angle measuring instrument into the die. Additionally, the recess for housing the angle measuring instrument is located in the side end surfaces of the split dies, so that angle measuring instruments can be installed at a plurality of locations in the die width direction of the upper die to detect the bend angle at the plurality of locations along a trace of a bent portion in order to easily obtain through accuracy for bending. The split dies with the angle measuring instrument interposed therebetween are adapted to be simultaneously changed between an arranged state and a non-selected state with respect to an operative position.
The present invention provides a method for operating a bending machine having one of the above described configurations of the present invention, the method being characterized by comprising measuring, during a bending process, an elevated and lowered positions of an upper die corresponding to the male die, a load acting on the upper die, and the bend angle of the work, measuring, after the bending process, the bend angle of the work after spring back after returning the upper die to some degree or releasing pressurization on the upper die, and obtaining a next correction value for an adjustable portion for controlling the bend angle for the bending machine, based on an interrelationship among the measured elevated and lowered positions of the upper die, the measured load acting on the upper die, the measured bend angle of the work, and the measured bend angle after spring back. The elevated and lowered positions of the upper die can be indirectly indicated in terms of time because they can be determined in terms of time if a speed curve for an elevating and lowering operations has previously been determined. The elevated and lowered positions of the upper die can be indicated in terms of time for an operation method according to another aspect of the present invention.
In the bending of work, predetermined relations occurs between the elevated and lowered positions of the upper die and the load acting on the upper die and the bend angle of the work, and affects the amount of spring back. Thus, by measuring the elevated and lowered positions of the upper die, the load acting on the upper die, and the bend angle of the work during bending and then measuring the bend angle after spring back to obtain the next correction value for the adjustable portion of the bending machine, which affects the bend angle, the next bending can be executed accurately. By measuring, after the bending, the bend angle after spring back after returning the upper die to some degree or releasing pressurization on the upper die, the angle present after spring back has occurred actually can be easily and accurately measured using the angle measuring instrument integrated into the upper die. This method for operating the bending machine may be used only during trial bending and the bending machine may subsequently be corrected using a next correction value obtained during the trial bending.
This method for operating a bending machine may comprise preparing a pattern table indicating a plurality of patterns into which the interrelationship between the elevated and lowered positions of the upper die and the load acting on the upper die and the bend angle of the work which are measured during the bending process has been classified, and correction value conversion data for each of the patterns which provide the next correction value for the adjustable portion corresponding to the bend angle after spring back, comparing the pattern table with the elevated and lowered positions of the upper die and the load acting on the upper die and the bend angle of the work which have been measured during the bending process, to select a corresponding pattern, and using the correction conversion data for the selected pattern to convert the bend angle after spring back measured after the bending process in order to obtain the next correction value for the adjustable portion.
Results of the inventors"" studies indicate that the relationship curve between the bending angle after spring back and the amount that the adjustable portion is adjusted to control the bending angle can be classified into a plurality of patterns based on the interrelationship between the elevated and lowered positions of the upper die and the load acting on the upper die and the bend angle of the work which occur during the bending process, and also indicate that the patterns have a common tendency. For example, patterning is possible based only on the relations between the above measured values despite a change in the thickness of the work or the material thereof. Accordingly, by preparing the pattern table and the correction value conversion data for each pattern, selecting a pattern based on the measured values obtained during the bending process, and obtaining the next correction value for the adjustable portion through a conversion using the correction value conversion data for the selected pattern, bending is easily and promptly achieved without the needs for complicated arithmetic operations. To obtain the next correction value using the correction value conversion data depending on the bending angle after spring back, the bending angle may be directly used or an error between the bending angle after spring back and a target angle may be used.
In this method for operating a bending machine, if the bending machine is of such a type that a lower die corresponding to the male die has a variable bottom surface height such that bending is carried out by lowering the upper die until the work has been pressed against a bottom surface of the lower die, then the adjustable portion is located at the bottom surface height of the lower die. The next correction value obtained from the correction value conversion data is a correction value for the bottom surface height.
In this method for operating a bending machine, if the bending machine is of a type that determines the bend angle by adjusting an amount that the upper die corresponding to the male die advances into the lower die, then the next correction value obtained from the correction value conversion data is a correction value for a target value for overstroke in which the upper die is lowered further from the elevated or lowered position of the upper die which corresponds to a target angle for the work bend angle.
In the method for operating a bending machine wherein the lower die has a variable bottom surface height, the pattern of the relationship between the elevated and lowered positions of the upper die and the load acting on the upper die and the bend angle of the work which all occur during the bending process may be classified in such a manner as to correspond to a stroke of the upper die from a load dip point to a target angle and a stroke thereof from the target angle to the lowest point. Results of the inventors"" studies indicate that more common patterning is achieved by classifying the pattern using strokes before and after the load dip point.
Another aspect of the invention provides a bending machine having one of the above described configurations of the present invention and having an adjustable portion for controlling the bend angle, the bending machine comprising the following learning control means.
The learning control means includes:
a pattern table indicating a plurality of patterns into which the interrelationship between an elevated and lowered positions of the upper die and a load acting on the upper die and the bend angle of the work which are measured during the bending process has been classified;
correction value conversion data for each of the patterns which provide the next correction value for the adjustable portion corresponding to the bend angle after spring back;
means for measuring the elevated and lowered positions of the upper die, the load acting on the upper die, and the bend angle of the work during the bending process;
means for measuring the bend angle of the work after the work has sprung back following returning of the upper die to some degree or releasing of pressurization on the upper die; and
correction value generating means for selecting the corresponding pattern from the pattern table based values of the elevated and lowered positions of the upper die, the load acting on the upper die, the bend angle of the work which have all been obtained during the bending process, and using the selected pattern to generate the next correction value for the adjustable portion corresponding to the bend angle after spring back, in accordance with the correction value conversion data.
The learning control means configured as described above enables implementation of the operation method according to the present invention which obtains the above described patterned next correction value.